The present invention relates to a system for writing data onto the thermally writing-type liquid crystal elements used for display equipment, and more particularly to a write control system suited for partially erasing the screen.
In the liquid crystal projection-type display device, the data after having been written are partially erased by simply erasing (writing) a portion as disclosed in the U.S. Pat. No. 3,836,243, for example.
According to the above system, however, no consideration has been given to drift or change in the positioning precision of thermal writing using a laser beam or the like beam or to a change in the power of the laser beam, and no consideration has been given to temperature drift by the thermal writing means (e.g., device for determining focal point of laser beam) or to drift with the lapse of time. Therefore, when it is desired to erase a thermally written portion from a pattern on the liquid crystal on which the data have been written in the previous time, the data are not often sufficiently erased from such a portion.